1. A Comparison of Varistors and Diodes

2. Varistors and Diodes
Special Note: These comparisons hold whether comparing discrete chips (TransGuard vs. diode) or arrays (MultiGuard vs. diode)

3. Summary of Advantages
Varistors have many advantages over diodes. These include:
Reliability
High temperature performance
Board space consumption
Bipolarity
Turn On Time
Filtering characteristics

4. Reliability Varistors survive many more ESD strikes than do diodes.
80000+
Pulses to
Failure
Energy

5. Reliability
A very small 0402 varistor provides more strike protection than a large SOT-23 diode
Suppression Method
# Strikes to failure
0402 TransGuard
>10000
0603 TransGuard
>80000
0805 TransGuard
1206 TransGuard
1210 TransGuard
SOT 23 Diode
23 Unidirectional
678 Bi-directional

6. Reliability Current The ceramic material is doped Zinc
Oxide where every grain is a Schottky
Diode. The structure between the plates
gives series/parallel diodes. The entire
volume dissipates energy.

7. High Temperature Performance
Varistors maintain their energy handling capabilities at higher temperatures than diodes
Varistor
Diode
Better temperature performance

8. Board Space Consumption
Discrete varistors are much smaller than discrete diodes:
0.067”
0.112”
0.020”
0.120”
Total Area = Total Area =
in in2
0402 TransGuard SOT 23 Diode
Reduction of 90% in board space required!

9. Board Space Consumption
Varistor arrays consumer much less boards space than diode arrays
0508 MultiGuard
SOT363 Diode Array
Reduction of 37% in board space required!
0.067”
0.098”
0.080”
0.087”
Total Area = in2
Total Area = in2

10. Board Space Consumption
Varistor arrays consumer much less boards space than diode arrays
SO-8 Bi-directional Diode Array
0508 MultiGuard
Reduction of >90% in board space required!
0.067”
0.298”
0.080”
.197”
Total Area = in2
Total Area = in2

11. Bipolarity Diodes protect in only one polarity
Many of the diode array packages protect only in one polarity
In order to protect in both polarities like the varistors, the number of elements is cut in half!
A 4-element unipolar diode array is only a 2-element bipolar diode array!

12. Turn On Time
The performance of an ESD protection device is measured by the amount of energy that the device allows to be passed to the circuit (or device) being protected.
The key measure of a device’s ability to reduce the amount of energy passed is measured by the turn of time of the device.
The turn on time of varistors is much less than the tune on time of a diode

13. Turn On Time Device Type Turn on Time (pS) 0402 TransGuard 417
673
0805 TransGuard
756
1206 TransGuard
818
1210 TransGuard
798
SOT 23 Diode
1380
Sub-nanosecond turn on time

14. Turn On Time ESD Waveform
TransGuard Turn-on Time ~ 400ps
Silicon TVS Turn-on Time ~ 1200ps
ESD Waveform
Unprotected Energy passed to circuit by the Diode

15. Filtering Characteristics
Diodes have very low capacitance, so they do not have filtering characteristics.
In fact, to achieve filtering and bipolar protection, 3 components must be used for the diode solution as compared to a single component for the varistor solution.

16. Filtering Characteristics
Again, varistors provide EMC filtering as seen in these S21 curves
Varistors can be manufactured to filter at different frequencies while still providing transient protection

17. Summary of Advantages
Varistors have many advantages over diodes. These include:
Reliability
High temperature performance
Board space consumption
Bipolarity
Turn On Time
Filtering characteristics